The present invention relates to a recording medium accommodation cassette and more particularly to a cassette in which a part of a cassette shell thereof is formed of a metallic plate.
Referring to FIGS. 1 to 3, the structure of a so-called 8-mm video cassette will be described as an example of a recording medium accommodation cassette.
Referring to the Figures, reference numeral 1 denotes an entire 8-mm video cassette and reference numeral 2 denotes a cassette shell (case) thereof. This cassette shell 2 is formed by combining an upper shell 3 and a lower shell 4 and fixing them to each other with screws and so on.
The cassette shell 2 accommodates therein a pair of reels, that is, a take-up reel 6 and a supply reel 7 such that they are rotatable.
The reels 6, 7 comprise hubs 6a, 7a, upper flanges 6b, 7b, and lower flanges 6c, 7c respectively and a magnetic tape 8 is wound around the hubs 6a, 7a of the reels 6, 7 respectively such that both ends of the tape 8 are fixed to the hubs 6a, 7a, respectively.
Tape guide portions 9a, 9b are provided on the left and right sides of the front portion of the lower shell 4. Then, a tape traveling path is formed such that the magnetic tape 8 derived from the supply reel 7 passes through the tape guide portion 9b, runs over the front part of the cassette shell, then passes through the tape guide portion 9a and finally is wound up by the take-up reel 6.
Reference numeral 10 denotes a lid for protecting the magnetic tape 8 which travels over the front part of the cassette shell. When the cassette is not in use, the lid 10 covers an exposed portion of the magnetic tape 8 over the front part of the cassette shell, while when the cassette is in use (when the cassette is inserted into a cassette deck), the lid 10 is rotated upward so that it opens so as to expose the magnetic tape 8.
Further, a pair of reel springs 11a, 11b (left, right springs) each being made of a leaf spring are attached to an internal surface of the upper shell 3 so that the reels 6, 7 are always pressed down to the lower shell 4 by the reel springs 11a, 11b thereby preventing the reels 6, 7 from being loose.
Further, within the cassette shell 2, a reel lock member 12 is assembled to a backward portion between both the reels 6 and 7. The reel lock member 12 is always urged toward the reels 6, 7 by the force of a reel lock spring 13. When the cassette is not in use, the reel lock member 12 engages engaging teeth 6d, 7d formed on outer peripheral edges of the lower flanges 6c, 7c of the reels 6, 7 so that the reels 6, 7 are locked from rotation thereby preventing the magnetic tape 8 from being loose.
In the tape cassette 1 having the above described structure, the cassette shell 2 is generally formed of resin (plastics) such as an ABS or the like. However, recently, formation of a part of the cassette shell with a metallic plate has been considered so as to further improve the stiffness of the cassette shell and also produce a luxurious feeling in its appearance.
As evident in FIGS. 2 and 3, a metallic plate 15 made of metal such as aluminum or the like is inserted into the central portion of a bottom portion 4a of the lower shell 4 supporting the reels 6, 7.
The metallic plate 15 is inserted upon molding of the lower shell 4. That is, upon molding of the lower shell 4, the metallic plate 15 is inserted within a molding die from the beginning and then with that condition, resin is injected into the molding die, so that the lower shell 4 having the metallic plate 15 integrally as shown in FIG. 3 is molded.
The metallic plate 15 to be inserted into lower shell 4 is provided with a plurality of punched holes 16 as shown in FIG. 3.
Here, 16a and 16b are reel driving shaft insertion holes, respectively, and 16c is a reel lock releasing member insertion hole.
The reel driving shaft insertion holes 16a, 16b are punched holes provided corresponding to the reels 6, 7, respectively. The reel driving shafts provided on the side of a cassette desk are inserted into these holes and engaged with the reels 6, 7, respectively.
The reel lock releasing member insertion hole 16c is a punched hole corresponding to the reel lock member 12. A reel lock releasing member provided on the cassette deck is inserted into this hole and then the reel lock member 12 is operated thereby unlocking the reels 6, 7.
These punched holes 16 are formed by punching the metallic plate 15 by means of press. This punching operation is outlined in FIGS. 5A-5C.
In FIGS. 5A-5C, reference numeral 20 denotes a punch and numeral 21 denotes a die having a concave portion 21a corresponding to the punch 20. Meantime, there is a slight clearance between the punch 20 and the die 21 such that an inner diameter of the concave portion 21a of the die 21 is slightly larger than an outer diameter of the punch 20.
With the metallic plate 15 set over the die 21 with the concave portion 21a as shown in FIG. 5A, when the punch 20 is descended from a higher position than the metallic plate 15 at a large pressing force, then as shown in FIG. 5B, until the punch reaches a middle portion in the thickness of the metallic plate 15, the metallic plate 15 is shorn between the punch 20 and the concave die 21, and finally the metallic plate 15 is punched out as shown in FIG. 5C in such a state that the metallic plate 15 is ruptured between the punch 20 and the concave die 21.
FIG. 4 shows an enlarged view of a condition of the punched hole 16 formed in the metallic plate 15 by punching work.
As evident from FIG. 4, the punched face (internal circumferential face) of the punched hole 16 is formed of a shear face 17 and a fracture face 18. Up to the middle in the punching direction, there is provided the shear face 17 which shows a straight surface produced by shearing, and which is followed by the fracture face 18 which shows sawtooth shape produced by fracture.
An end edge portion 17a of the shear face 17 of the punched hole 16 is formed in a mild round corner shape deformed by the pressing force upon punching, while an end edge portion of the fracture face 18 has a so-called punch-out burr 19 produced upon fracture, which protrudes sharply. A protrusion amount h.sub.1 of the punched-out burr 19 differs depending on a thickness of the metallic plate 15. If the thickness of the metallic plate 15 is 1.2-1.5 mm, h.sub.1 is about 20-30 .mu.m.
Thus, if as shown in FIGS. 6, 7, the punched-out burr 19 is in contact with a structural component in the cassette or the lower flanges 6c, 7c of the reels 6, 7, in this example and hence friction is generated between the burr 19 and the lower flanges 6c, 7c of the reels 6, 7 so that the resin of the lower flanges 6c, 7c of the reels 6, 7 is shaved thereby producing shaving powders. Further, if the shaving powders adhere to the magnetic tape, it may cause a dropout in recording and reproduction signals thereby deteriorating largely the reliability.
Although there is a method of removing the burr 19 on the metallic plate 15 so as to solve the above problem, it takes a long time and labor to remove the burr completely, so that production cost of the metallic plate 15 is increased. Thus, this is not a practical solution.
Further, although narrowing the clearance between the punch 20 of the press and the concave die 21 is effective as a method of suppressing an occurrence of the burr, in this case, the service life of the die remarkably shortens, so that this method is not suitable for mass production thereof. Still further this method is not capable of removing the burr completely.